Generating random chunks from array in javascript

Question

I have an array of objects which looks like this:

[
    {
      pVerb: "ask somebody out",
      meaning: "invite on a date"
    },
    {
      pVerb: "ask around",
      meaning: "ask many people the same question"
    },
    {
      pVerb: "add up to something",
      meaning: "equal"
    },
    {
      pVerb: "back something up",
      meaning: "reverse"
    },
    {
      pVerb: "back somebody up",
      meaning: "support"
    },
    {
      pVerb: "blow up",
      meaning: "explode"
    }
  ]

I need to iterate trough every object and generate smaller array chunks that should:

Be of a length of 3
Contain current object entry of pVerb
Be placed on random positions

something like following:

[
  [
    "!ask somebody out!",
    "add up to something",
    "back something up"
  ],
  [
    "add up to something",
    "!ask around!",
    "blow up"
  ],
  [
    "blow up",
    "back somebody up",
    "!add up to something!"
  ]
]

Currently I have something like this but it does not check for duplicate entries or randomize the positions:

const randomNumber = (max: number, min: number) => {
      const num = Math.floor(Math.random() * (max - min + 1)) + min;
      return num;
    };

    const array: any[] = [];
    for (const n of array) {
      array.push([
        n.meaning,
        array[randomNumber(0, array.length)]
          .meaning,
        array[randomNumber(0, array.length)]
          .meaning
      ]);
    }

TL:DR

I need array of chunks where a chunk would be [pVerb of first object, any other two pVerbs from any other two objects(unique)] next chunk would have [pVerb of second object, ...] etc.

To generate a unique random sequence on your array, [check this](https://stackoverflow.com/questions/196017/unique-non-repeating-random-numbers-in-o1) — Leonardo Alves Machado, Oct 05 '18 at 11:11
I'm not sure what you meant by randomize the positions - you want to shuffle the array when it is filled? — Leonardo Alves Machado, Oct 05 '18 at 11:13
To me, it doesn't make much sense, since the array will be generated randomly. But, if you would like to shuffle, you can just loop one through the array, generate a random index and switch elements... — Leonardo Alves Machado, Oct 05 '18 at 11:18
Should the first entry remain in order like it does in your example, with only the last two being shuffled? — Ry-, Oct 05 '18 at 11:18
@Ry- no, the idea is that all chunks should contain appropriate pVerb, so first one contains the one from first object, second from second obj ,etc. — Dimitry Ivashchuk, Oct 05 '18 at 11:26

score 1 · Accepted Answer · answered Oct 05 '18 at 12:04

You can get a randomly ordered random selection of three elements from the array with the help of a shuffle:

const partialShuffle = (values, count) => {
  for (let i = 0; i < count; i++) {
    const j = Math.floor(Math.random() * (values.length - i)) + i;
    [values[i], values[j]] = [values[j], values[i]];
  }
};

const nums = [1, 2, 3, 4, 5, 6];
partialShuffle(nums, 3);
console.log('' + nums.slice(0, 3));
partialShuffle(nums, 3);
console.log('' + nums.slice(0, 3));
partialShuffle(nums, 3);
console.log('' + nums.slice(0, 3));

Now that you have three random values in an array, you want to make sure one of them is the current value – the one that corresponds to the pVerb. Check if it’s in there.

If it’s already present, nothing more needs to be done.
If it isn’t present, pick a random item to replace with it.

const randomTripleIncluding = (values, value) => {
  partialShuffle(values, 3);
  const triple = values.slice(0, 3);

  if (!triple.includes(value)) {
    triple[Math.floor(Math.random() * 3)] = value;
  }

  return triple;
};

This messes up the order of the array, so you’ll want to make a copy exclusively for shuffling use, since you’re iterating over the original array. All told, with types:

const partialShuffle = (values: any[], count: number) => {
  for (let i = 0; i < count; i++) {
    const j = Math.floor(Math.random() * (values.length - i)) + i;
    [values[i], values[j]] = [values[j], values[i]];
  }
};

const randomTripleIncluding = <T>(values: T[], value: T): T[] => {
  partialShuffle(values, 3);
  const triple = values.slice(0, 3);

  if (!triple.includes(value)) {
    triple[Math.floor(Math.random() * 3)] = value;
  }

  return triple;
};

const input = [
  {pVerb: "ask somebody out", meaning: "invite on a date"},
  …
];

const scratchInput = input.slice();

const result = input.map(n => randomTripleIncluding(scratchInput, n));

God bless you! Worked as expected – Dimitry Ivashchuk Oct 05 '18 at 12:14 — Dimitry Ivashchuk, Oct 05 '18 at 12:14

Generating random chunks from array in javascript

TL:DR

1 Answers1